Braving chest-deep water, boot-sucking mud and punishing heat in the cypress swamps of West Tennessee, biologists from the Tennessee Aquarium Conservation Institute and several partner organizations are trying to determine whether a dinosaur-like turtle could be on the downward slide to extinction.
The Alligator Snapping Turtle is North America’s largest freshwater turtle species. In the mid-20th century, it was heavily harvested for its meat, and wild turtles are still being removed to supply the pet trade in the U.S. and Southeast Asia. After weathering decades of these parallel threats, no one is quite sure how many Alligator Snapping Turtles remain in Tennessee.
Determining the population health of this shelled behemoth is a priority for the United States Fish and Wildlife Service, which is considering listing the Alligator Snapping Turtle under the Endangered Species Act. To determine whether this tri-ridged, fierce-beaked reptile warrants that designation, the service has enlisted the help of scientists to seek it out in its native swamps and rivers.
In April 2016, Tennessee Aquarium Conservation Institute biologist Dr. Josh Ennen and representatives from the Tennessee Wildlife Resources Agency and Southern Missouri State University began a three-year research project to evaluate the distribution and population status of Alligator Snapping Turtles in West Tennessee.
Using passive integrated transponder (PIT) tags, the researchers are able to uniquely identify any turtles they recover. By visiting the same locations over time and rescanning the turtles they capture, researchers will be able to estimate population numbers in a given area.
Alligator Snapping Turtles have struggled against many threats, but fighting to survive is a position in which many turtles find themselves. About half of all turtles species are designated as some degree of vulnerable.
“Turtles are one of the most-imperiled vertebrate groups,” Ennen explains. “They have the kind of life history that you can’t overexploit populations because they’re long-lived and slow to mature, so they can’t keep up with that kind of harvesting pressure.”
As they conduct their population assessment, researchers also are gathering data to determine whether Alligator Snapping Turtles and other species with which they share their habitat are becoming unsafe for human consumption due to the build-up of mercury and other dangerous substances in their bodies.
Particularly due to their longevity, turtles can serve as a kind of long-term litmus test for environmental conditions. By analyzing clippings of turtles’ claws, researchers can evaluate the concentration of toxic heavy metals in the surrounding habitat.
If those levels are determined to be dangerously high, it could reflect a general downward trend in local water quality. Ironically, Ennen says, Alligator Snapping Turtles that survived being hunted or captured for the pet trade could be preserved thanks to environmental contamination that renders them unsafe to eat.
“Those toxicity levels will serve as an indicator of what the water is like, both for other animals and for humans as well,” Ennen says. “Turtles can be bio-indicator species, so if there’s a contamination issue with turtles, you can have a contamination issue with fish and other animals.”
Moving ahead, Ennen says, the hope is to seek an extension for the project to investigate rivers and swamps in Middle Tennessee and, in the near future, to begin using radio tracking to better understand the habitat use of juvenile Alligator Snapping Turtles in the study area.
“We need to know where this species is found in the landscape and how it utilizes the habitat where it is found,” he says. “By extending our research of these long-lived animals, we’ll be able to develop a more complete picture of their numbers and individual health. That way, we’ll be better prepared to write a recovery plan if we determine these turtles should be listed as endangered.”

For the Barrens Topminnow, conditions couldn’t get much worse.
After months with little to no rain, the Middle Tennessee stream that serves as a vital habitat to one of the last remaining wild populations of endangered Barrens Topminnows has all but dried up. The once sparkling water has been reduced to a series of stagnant pools connected by an anemic trickle of murky water.
After monitoring the ecological impact of the region’s exceptional drought for months, representatives from the Tennessee Aquarium Conservation Institute (TNACI) and U.S. Fish and Wildlife Service visited this critical stream on a farm north of Manchester, Tenn., to determine how bad conditions were and whether a rescue effort was warranted.
As he looked out on the drought-ravaged scene, however, Tennessee Aquarium Aquatic Biologist Dr. Bernie Kuhajda realized the situation was even worse than anticipated.
“I thought it’d be dry. I had no idea there’d be practically no water here,” Dr. Kuhajda said. “I don’t have a lot of hope. This was by far the healthiest population of Barrens Topminnows anywhere. This is pretty cataclysmic.”
Despite its diminutive size and limited range, the Barrens Topminnow is part of a delicate ecosystem. Ensuring its survival is crucial to preserving the natural balance of the entire waterway, said Clay Raines, Tennessee Aquarium reintroduction biologist.
“All we know for sure is that the more species you have, the more stable the ecosystem is,” he said. “You lose that chain, and no one can say, for certain, what those foundational species are — who’s most important and who’s least important — in that ecosystem. We have to value all aquatic life equally and preserve what we can.”
The Middle Tennessee stream system, a tributary waterway of Lewis Creek, once contained hundreds of fish and served as habitat to a large percentage of the two remaining wild populations of Barrens Topminnows known to exist.
As they sifted through the grubby catch of each seine net haul from the puddle-thin water, however, the team were finding found just a handful of Barrens Topminnows. Worse yet, they were disconcerted to discover plentiful Western Mosquitofish, a hardy invasive species which preys on Barrens Topminnow young. Mosquitofish had not been found in this tributary before.
“The presence of Mosquitofish getting in these upstream headwater habitats is pretty disheartening,” said the Tennessee Aquarium’s Assistant Curator of Fishes Matt Hamilton, whose involvement in the Barrens Topminnow recovery program dates back to 1999.
Once Mosquitofish begin to reproduce, he said, the demise of the Barrens Topminnows will become an almost foregone conclusion.
“It’ll be a numbers game at that point,” he said. “Mosquitofish numbers are going to increase, and the Barrens Topminnows are going to decrease. These topminnows are a short-lived species, so it won’t be long until they are gone.”
When environmental conditions become bad enough to place an entire species’ survival at risk, conservation scientists sometimes resort to bringing an entire wild population into human care to create an “ark population” to safeguard against the possibility of extinction.
Within the Southeast, many such captive populations and propagation programs soon will be housed at TNACI’s flagship freshwater field station near downtown Chattanooga. This state-of-the-art facility on the banks of the Tennessee River opened on Oct. 27 and already serves as the headquarters for propagation programs for Southern Appalachian Brook Trout and Lake Sturgeon.
After two and a half hours of work and dozens of seine hauls, the field team recovered just 64 Barrens Topminnows, an amount that previously could have been acquired in a single net drag. These individuals were placed in bags of clean, oxygenated water and taken to a TNACI facility as part of a new ark population.
“Without taking this last-resort action, this population would be gone forever,” said Dr. Kuhajda. “Now there’s hope to keep this genetically distinct population intact with the long-term goal of re-establishing a healthy population here again.”
The drought conditions are having a dramatic impact on many species throughout the Southeast’s extremely bio-diverse waterways.
After witnessing the devastated conditions they found in Middle Tennessee, TNACI representatives will visit sites on Walden Ridge near Spring City, Tenn. This is one of the few remaining locations where the federally endangered Laurel Dace is found. If the streams conditions prove to be as bone-dry as the spring-fed waters in Middle Tennessee, whatever Laurel Dace remain will be rescued for another ark population.
In the Cherokee National Forest, the ongoing exceptional drought and record-high temperatures have resulted in streams that are shallower, slower-flowing and warmer. These conditions are wreaking havoc on the native Southern Appalachian Brook Trout, whose habitat was already just 12 percent of its historical extent.
Trout, which prefer cooler water, are concentrating in deeper pools. At lower elevations, their proximity to one another is leading to increased rates of disease and predation, said Jim Herrig, a forest aquatic biologist with the U.S. Forest Service Forest. “When we get to higher elevations, the larger streams are suffering really bad,” he said. “The water is getting so warm that the trout aren’t able to persist.”
The Southern Appalachian Brook has been the subject of a long-term, collaborative restoration effort between TNACI, the U.S. Forest Service and the Tennessee Wildlife Resources Agency. Thanks to the reduced water flow, however, the facilities involved in this effort have been largely shuttered.
“Nobody is going to be raising any Brook Trout this year,” Herrig said.
The U.S. Fish and Wildlife Service has found a similarly deadly byproduct of the drought in a mass die-off of mussels in the Clinch River system of Northeast Tennessee and Southwest Virginia, where water levels are a fraction what they were in wetter months.
“It’s definitely the driest we’ve ever seen it, and it’s been dry all around the state,” said Stephanie Chance, a USFWS listing and candidate conservation biologist, who assisted with the Barrens Topminnow recovery. “It’s troubling.”
The work of conserving native species is complex and, in times like these, frustrating for biologists. Healthy populations of aquatic animals can deal with natural cycles that bring periods of drought, disease or other environmental stresses. But, when a species is already on the brink, the tipping point is easier to reach. Kuhajda believes shoring up these fragile ecosystems requires considering the important role fresh water plays in our daily lives and doing everything we can to safeguard it.
“When our rivers and streams dry up, people really focus on water,” he said. “But we should be thinking about our most important resource throughout the year.”
About Barrens Topminnows:
Size: Up to 4 inches
Range: Found only on the Barrens Plateau of Middle Tennessee
Conservation Status: Endangered in Tennessee and currently under review for listing by the U.S. Fish and Wildlife Service. If approved, this species would be protected under the Endangered Species Act.
Threats: The introduction of the Western Mosquitofish, which eats very young Barrens Topminnows, drought, water quality, and alteration of springs and small streams.
Conservation Efforts: The Tennessee Aquarium monitors the Barrens Topminnow population and has worked with conservation partners to release more than 44,000 Barrens Topminnows into their natural habitat. Aquarium guests can see this ongoing work inside the Barrens Topminnow Lab Exhibit, which is located in the River Journey building.